Db command improvements and new features

This PR contains three changes/features.

1. `db:maintain:check-tables` has been refactored to run properly on InnoDB tables.
2. Added command db:variables to show server variables
3. Added command db:status to show the current server status.

I left some todos in the code which are pretty time consuming but can be solved e.g. on the hackathon.

If there should be something weird (code, naming, etc) please comment :-)

Otherwise please merge :-) Thanks!

The following printscreens shows the commands more clearly.

![screen shot 2014-11-03 at 4 08 47 pm](https://cloud.githubusercontent.com/assets/372027/4878900/475e5ff4-631c-11e4-8b1d-6772685bfacf.png)
![screen shot 2014-11-03 at 4 37 30 pm](https://cloud.githubusercontent.com/assets/372027/4878902/475f7c18-631c-11e4-8197-c0f8c722eb05.png)
![screen shot 2014-11-03 at 4 37 48 pm](https://cloud.githubusercontent.com/assets/372027/4878899/475cac9a-631c-11e4-8ad8-790f6f2fe527.png)
![screen shot 2014-11-03 at 4 38 17 pm](https://cloud.githubusercontent.com/assets/372027/4878903/4761688e-631c-11e4-9cd8-b7f851294ef8.png)
![screen shot 2014-11-03 at 4 38 34 pm](https://cloud.githubusercontent.com/assets/372027/4878901/475eee4c-631c-11e4-9b4a-57ae9018a8af.png)
![screen shot 2014-11-03 at 4 38 50 pm](https://cloud.githubusercontent.com/assets/372027/4878904/4764ce52-631c-11e4-9d49-08e0c37be332.png)
![screen shot 2014-11-03 at 4 39 56 pm](https://cloud.githubusercontent.com/assets/372027/4878905/478534da-631c-11e4-8fc2-9d95a88b621f.png)